1. Field of the Invention
The present invention relates to an apparatus driving a driven member by a DC brushless motor.
2. Description of the Related Art
FIG. 13 is a block diagram for driving the carriage of a conventional common inkjet recording apparatus. In FIG. 13, a belt 2 is integrally connected to a carriage 1 on which a recording head (not illustrated) is mounted. Arranged at one end of the belt 2 is an idler pulley 3 rotatably supported while maintaining tension with respect to the belt 2. Arranged at the other end of the belt 2 is a driving pulley 5. The driving pulley 5 is integrally engaged with a carriage motor (hereinafter referred to as the “carriage (CR) motor”) 4 serving as a drive source. Thus, the carriage 1 is supported so as to be slidable in response to the rotation of the CR motor 4. Printing on a medium such as paper is conducted by discharging ink from a recording head while performing scanning with the carriage 1 in response to the rotation of the CR motor 4.
As the CR motor 4, there is employed a brushless electric motor called a DC brushless motor. The CR motor 4 contains a plurality of Hall elements 6 for detecting the timing with which switching of energization of each coil in the CR motor 4 is effected. The plurality of Hall elements 6 detect a region where a rotor magnetic pole in the CR motor 4 is situated. Each Hall element 6 outputs a detection signal indicating the timing with which energization switching for each coil in the CR motor 4 is effected. The detection signal also indicates the region where the rotor magnetic pole in the CR motor 4 is situated.
To detect the position of the carriage 1 in the sliding direction (scanning direction), there is arranged a linear encoder 8. The linear encoder 8 includes a scale 8 and a sensor main body 1a. The scale 8a is arranged on the printer main body side so as to extend in the scanning direction of the carriage 1. The scale 8a is provided with a plurality of slits arranged at predetermined intervals. The sensor main body 1a, which is a sensor having a light emitting portion and a light receiving sensor, is mounted to the carriage 1. As the carriage 1 moves, the sensor main body 1a detects the slits of the scale 8a. Each time it detects a slit, the sensor main body 1a outputs a detection pulse. The linear encoder 8 indicates the position of the carriage 1 by the number of output detection pulses.
On the printer main body side, a read-only memory (ROM) 10 stores a program necessary for driving the carriage 1 and other related members through a predetermined operation, and data such as initial values. A microprocessor unit (MPU) 9 reads the program and data from the ROM 10, and performs necessary computation while temporarily storing data being computed in an external random-access memory (RAM) 11. Further, the MPU 9, which also serves as an external communication unit, communicates with an external apparatus via an interface 12, conducting various kinds of processing.
Detection pulses, which constitute positional information on the carriage 1, are input to the MPU 9 via a buffer (not illustrated). Inside the MPU 9, a pulse counting unit 9a counts the detection pulses, and outputs the count value of the detection pulses to an acceleration/deceleration computation unit 9b. 
Based on the count value of the detection pulses, the acceleration/deceleration computation unit 9b outputs a drive command for the CR motor 4, such an acceleration/deceleration signal and a rotating direction signal. The drive command is input to a CR motor driving circuit 7 via a gate array 13.
The CR motor driving circuit 7 controls the rotation of the CR motor 4 in accordance with the drive command from the acceleration/deceleration computation unit 9b and the detection signal from each Hall element 6. As a result, the carriage 1 performs a predetermined operation.
Such a construction is not restricted to an ink jet recording apparatus but is also applicable to apparatuses controlling the movement of a driven member by using a linear encoder.
FIGS. 14A through 14D are diagrams illustrating the output of each Hall element 6 in the conventional common CR motor (DC brushless motor) 4, the output from the CR motor driving circuit 7 to each coil in the CR motor 4, and the voltage condition of each coil in the CR motor 4.
The CR motor 4, which is a DC brushless motor, is driven in a stable manner by varying the energization combination in each coil in the CR motor 4 according to the high/low (H/L) combination in the output of each Hall element 6 in the CR motor 4. As the coils in the CR motor 4, there are used Y-connection coils U, V, and W, one end of each of which is subjected to common connection. In the following, the other end of the coil U will be referred to as the coil U terminal, the other end of the coil V will be referred to as the coil V terminal, and the other end of the coil W will be referred to as the coil W terminal.
As the plurality of Hall elements 6, there are used Hall elements u, v, and w. The Hall elements u, v, and w generate a sinusoidal wave assuming positive potential when an N-pole in the rotor in the CR motor 4 comes close thereto and negative potential when an S-pole in the rotor comes close thereto. FIG. 16 illustrates the driving circuit for the brushless motor discussed in U.S. Pat. No. 4,882,511. A pair of coils (coils 21 and 22; coils 23 and 24; coils 25 and 26) are connected in a Y-shape. The input terminals of driver amplifiers 46, 47, and 48 are respectively connected to position sensors 42, 43, and 44. The output terminals of the driver amplifiers 46, 47, and 48 are respectively connected to the coils.
In the Hall element output chart of FIG. 14A, the solid line indicates the output of the Hall element u, the broken line indicates the output of the Hall element v, and the alternate long and short dash line indicates the output of the Hall element w. The respective outputs of the three Hall elements u, v, and w are out of phase with respect to each other by 120 degrees in terms of energization angle.
The rectification table (energization table) of FIG. 14B illustrates the relationship between the outputs of the Hall elements u, v, and w and the pattern of energization of the coil U terminal, the coil V terminal, and the coil W terminal. According to the rectification table, in a combination in which the output of the Hall element u is “H” (at high level), the output of the Hall element v is “L” (at low level), and the output of the Hall element w is “H”, the CR motor driving circuit 7 outputs “L”, “H”, and “OPEN” signals to the coil U terminal, the coil V terminal, ant the coil W terminal, respectively. In the rectification table, “OPEN” is shown as “N.C.”. The signals from the CR motor driving circuit 7 are referred to as the coil energization voltage waveform.
In the waveform chart of FIG. 14C, U-C, V-C, and W-C shown in the explanatory note indicate a counter electromotive voltage waveform representing the coil U terminal, the coil V terminal, and the coil W terminal as seen from a common terminal C. Referring to the waveform diagram of FIG. 14C, in the first Hall element output combination, a large counter electromotive voltage in the negative direction has been generated in the coil U; a large counter electromotive voltage in the positive direction has been generated in the coil V; and, in the coil W, the counter electromotive voltage is at low level. This means, in terms of efficiency, that electric current is passed from a phase in which the counter electromotive voltage in the positive direction is large to a phase in which the counter electromotive voltage in the negative direction is large.
The waveform diagram of FIG. 14D shows the waveform of the voltage from the CR motor driving circuit 7; it shows that, by setting the coil V terminal (broken line) to H level and by setting the coil U terminal (solid line) to L level, energization is effected from the coil V terminal to the coil U terminal. Similarly, as illustrated, there are other five combinations of the outputs of the Hall elements u, v, and w (see the rectification table); through six combinations in total, rectification is continuously effected on the coils U, V, and W, and the rotation of the CR motor 4 continues.
FIGS. 15A and 15B are diagrams which re-represent the U phase (coil U) of the coil counter electromotive waveform and the energization voltage waveform illustrated in FIGS. 14C and 14D. The graph of FIG. 15A illustrates the counter electromotive voltage waveform between the common terminals of the U-phase coil (coil U terminals), and the graph of FIG. 15B illustrates the energization voltage waveform of the U-phase coil (coil U). Of the energization voltage waveform, the portion thereof that is at “0” indicates the portion where the 0 side (L side) switching element connected to the coil U terminal of the U-phase coil is on, drawing the potential of the U-phase coil to the 0 side (L side). Of the energization voltage waveform, the portion thereof that is at “1” indicates the portion where the 1 side (H side) switching element connected to the coil U terminal of the U-phase coil is on, drawing the potential of the U-phase coil to the 1 side (H side).
When the counter electromotive voltage waveform is large on the negative side, large torque is generated by drawing the potential of the coil to the L side; and, when the counter electromotive voltage waveform is large on the positive side, large torque in the direction opposite to the L side is generated by drawing the potential of the coil to the H side.
In FIGS. 15A and 15B, the portions that are at “0.5” indicate that the two switching elements connected to the coil U terminal of the U-phase coil are both off. In this state, no positive energization to the U-phase coil is being effected.
The combination of the Hall elements in the DC brushless motor is fixed while the rotor magnetic pole in the DC brushless motor is situated in a certain region. Thus, in the state in which the rotor in the DC brushless motor is rotating, there is no change in the combination of the output levels of the Hall elements, even if the position of the rotor inside the DC brushless motor is somewhat changed.
As described above, by using a linear encoder, it is possible to detect fluctuation in the speed of a moving driven member. However, in the conventional method in which the DC brushless motor is controlled based on the outputs of the Hall elements, it is impossible to perform control to suppress this fluctuation in speed.